The present invention relates to a power-feed control apparatus provided in a vehicle for controlling turn-on or off operations of electrical loads such as lamps, motors, and so on, using power semiconductor elements with a protection function to detect an anomaly in a circuit including each load and to interrupt the power-feed to the load in the circuit, and especially relates to a power-feed control apparatus suitable for a vehicle in which electrical loads are incorporated being controlled by a network system using a serial-transmission line.
In a general conventional method, a current flow fed to a load is detected, and if the current flow excessively increases, the current flow is interrupted. This method is implemented with MOS-FETs in techniques disclosed in Japanese Patent Application Laid-Opens Sho. 61-2611920, Sho. 62-11916, Sho. 62-143450, and Sho. 63-87128.
Furthermore, a technique disclosed in Japanese Patent Application Laid-Open Hei. 8-303018 permits a large starting current of a load such as a lamp, and interrupts a power-feed to a load if a short-circuit anomaly is detected at the load.
The above conventional techniques cannot deal with an anomalous consumption of energy in a battery due to a rare short-circuit (incomplete short-circuit) in a load, a locking anomaly of a motor due to an extraneous part inserted into the motor, an anomaly (generation of heat, inflammation, etc.) of the whole control system due to accumulation of heat slightly and continuously generated in power lines, and so on.
That is, if a power element with only one protection function based on current or temperature is designed so that the power element does not interrupt a power-feed to a load connected to the power element during the initial period with a large starting current flow, a comparatively small and anomalous change of current flowing in the power element in a steady-state cannot be detected and dealt with. Further, in a power-feed control system in which an anomaly in temperature or current is detected and the interruption of power-feed is performed for each load, the composition of the control system becomes complicated and expensive. In a method in which a current detection resistor is serially connected to a load, the power loss at the current detection resistor is large, which increases the waste heat generation.